In a conventional alternator with a vacuum pump, for example, as disclosed in U.S. Pat. No. 3,628,328, the vacuum pump is generally attached to a rear side of the alternator, that is a side opposite to a front side where a driven pulley is provided.
In the conventional alternator of this type, however, an alternator shaft and other associating parts must be designed larger since a driving force for the vacuum pump is transmitted through a power transmission mechanism of the alternator. For example, in an alternator driven by a belt, a diameter of an alternator shaft must be designed larger since a torque applied to the alternator shaft is increased, and furthermore a larger bearing for the alternator shaft must be employed since a radial load applied to the bearing is increased in accordance with the increase of the belt tension.
In the conventional alternator of the above type, brushes for supplying electrical power to the rotor are also arranged at the rear side of the alternator, which may cause such a problem that the brushes are tainted and worn away when the lubricating oil leaks out of the pump chamber.
Furthermore, it is disadvantageous in the prior art alternator with a vacuum pump in that when a volume or a size of the vacuum pump should be changed, specifications of the alternator must be accordingly modified.